Persons having facial nerves or muscles damaged by disease or injury oftentimes suffer from varying degrees of facial paralysis or abnormal facial movements, such as synkinesis (involuntary or inappropriate facial motion associated with voluntary facial motion), contracture or hemifacial spasms. Treatment of facial paralysis and abnormal facial movements may include physical therapy, neurotrophic drugs and/or reconstructive surgery. Measuring and quantitating facial movements is useful in detecting, characterizing and treating facial paralysis or abnormal facial movements. Quantitative information is also helpful in evaluating facial symmetry and planning reanimation procedures.
Several ordinal methods exist for qualifying facial movements. Most notably is the John W. House, M.D. facial nerve grading system ("House Scale"), based on prior facial grading systems, which provides a gross scale using six grades (I-VI) to subjectively categorize overall facial function. See, J. House, Facial Nerve Grading Systems, 93 Laryngoscope 1056 (1983), the disclosure of which is incorporated herein by reference. Table 1 sets forth the House Scale definitions of varying degrees of facial function corresponding to the six grades. Secondary facial defects such as synkinesis, mass action and hemifacial spasms are also considered and included in the overall grading of facial movement.
TABLE 1 __________________________________________________________________________ Grade Definition __________________________________________________________________________ I. Normal Normal facial function in all areas. II. Mild dysfunction Slight weakness noticeable only on close inspection. At rest: normal symmetry and tone. Mo- tion: some to normal movement of forehead; ability to close eye with minimal effort and slight asymmetry; ability to move corners of mouth with maximal effort and slight asymmetry. No synkinesis, contracture or hemifacial spasm. III. Moderate dysfunction Obvious but not disfiguring difference between two sides; no functional impairment; noticeable but not severe synkinesis, contracture and/or hemifacial spasm. At rest: normal symmetry and tone. Motion: slight to no movement of forehead; ability to close eye with maximal effort and obvious asymmetry; ability to move corners of mouth with maximal effort and obvious asym- metry. Patients with obvious but not disfiguring synkinesis, contracture, and/or hemifacial spasm are Grade 3 regardless of degree of motor activity. IV. Moderately severe dysfunction Obvious weakness and/or disfiguring asymmetry. At rest: normal symmetry and tone. Motion: no movement of forehead; inability to close eye completely with maximal effort; asymmetrical movement of corners of mouth with maximal effort. Patients with synkinesis, mass action, and or hemifacial spasm severe enough to interfere with function are Grade 4 regardless of de- gree of motor activity. V. Severe dysfunction Only barely perceptible motion. At rest: possible asymmetry with droop of corner of mouth and decreased or absent nasal labial fold. Motion: no movement of forehead; incomplete closure of eye and only slight movement of lid with maximal effort; slight movement of corner of mouth. Synkinesis, contracture, and hemifacial spasm usually absent. VI. Total paralysis Loss of tone; asymmetry; no motion; no synkinesis, contracture, or hemifacial spasm. __________________________________________________________________________
Under the House Scale, evaluation of a patient is expressed as a fraction where the numerator is the patient's score and the denominator is the maximum possible score. Thus, a patient with moderately severe facial dysfunction will have a score of IV/IV.
The House Scale also includes a method for measuring facial movement to assist an investigator in placing a patient in the proper grade. See, J. House, D. Brackmann, Facial Nerve Grading System, 93 Otolaryngology--Head and Neck Surgery 146 (1985), the disclosure of which is incorporated herein by reference. Specifically, the patient's eyebrow movement and movement of the corner of the mouth on the affected side of the face is measured and then compared to the measured movements on the unaffected side of the face. A one centimeter scale having 0.25 centimeter divisions is used to measure the movements for a total possible score of 8 (4, or 1 centimeter for the mouth and 4, or 1 centimeter, for the eyebrow). As shown in Table 2, the numeric scores are converted to the six grade scale. This method for measuring facial movement is similar to the method proposed by Derald E. Brackmann, M.D., and David M. Barrs, M.D. See, D. Brackmann, D. Barrs, Assessing Recovery of Facial Function Following Acoustic Neuroma Surgery, 92 Otolaryngology--Head and Neck Surgery 88 (1984), the disclosure of which is incorporated herein by reference.
TABLE 2 ______________________________________ Function Estimated Grade Description Measurement (%) function (%) ______________________________________ I Normal 8/8 100 100 II Slight 7/8 76-99 80 III Moderate 5/8-6/8 51-75 60 IV Moderately 3/8-4/8 26-50 40 severe V Severe 1/8-2/8 1-25 20 VI Total 0/8 0 0 ______________________________________
The International Assessment Scale, based on the House Scale, was adopted at the Fifth International Symposium on the Facial Nerve in Bordeaux in 1984. This Scale uses six grades (I-VI) similar to the grades of the House Scale to subjectively categorize overall facial function. See, R. Balliet, Manual of Physical Therapy, Ch. 5, Facial Paralysis and Other Neuromuscular Dysfunctions of the Peripheral Nervous System, 175, 181 1989, the disclosure of which is incorporated herein by reference.
The University of Wisconsin Facial Paralysis Clinical Assessment Scale (the "Wisconsin Scale"), is a more complicated assessment scale requiring estimates of voluntary and spontaneous facial movement, and resting facial tone as a percentage of normal facial movement. See, Balliet, supra, at 183. These estimates are difficult to make, but electromyographic measurements of the facial movements and resting tone generally improve the accuracy of the assessment. Synkinesis is also graded on a scale of zero to four (none to severe) and other muscle responses, such as tics and spasms are noted. The estimates for the voluntary and spontaneous facial movements and resting tone are averaged and weighted relative to importance and then added. The resulting scores are compared to other assessment scales, such as the International Assessment Scale. Analyzing facial movements based on the Wisconsin Scale is complicated, time consuming and expensive.
The House Scale and its modifications are useful because they provide a global clinical evaluation of dynamic facial movement which is readily communicable between clinicians. These ordinal scales, however, fail to quantitate actual facial movements, measure the movement vector for reanimation procedures and provide a means for storing facial movement data. Further, these scales remain limited in that they are dependent upon the investigator's perception to recognize facial defects and analyze the patient's disability.
Quantitative methods for assessing facial motion have also been developed. For example, Jansen et al. developed a lip-length index which measures the difference between the intercommissural distances of the lips at rest and after maximal smile and a snout index which measures the difference between the intercommissural distances of the lips at rest and after maximal pucker. See, C. Jansen, P. DeVriese, F. Jennekens, H. Wijnne, Lip-Length and Snout Indices in Bell's Palsey: A Comparison With The House Grading System, 111 Acta Otolaryngology 1965 (1991), the disclosure of which is incorporated herein by reference. These indices are continuous variables suitable for statistical evaluation. Further, a high correlation exists between the indices and the House Scale suggesting that these assessment tools are complementary. The lip-length and snout indices, however, are limited in that they only provide information pertaining to peri-oral function.
Steven A. Burres, M.D., derived three parameters of facial function based on linear measurements of skin landmarks and integrated electromyography ("EMG") of facial musculature to quantify facial movement. See, S. Burres, Facial Biomechanics: The Standards of Normal, 95 Laryngoscope 708 (1985), the disclosure of which is incorporated herein by reference. Specifically, Burres measured the facial movements of thirty subjects using calipers and electromyography to derive (1) the Linear Measurement Index ("LMRI") (proportional to maximum force), (2) EMG symmetry (level of integrated EMG compared to unaffected side), and (3) Peak Electromechanical Ratio ("PEMR") (correlation of motor unit electrical activity with motion). Further, Buttes concluded that a linear relationship exists between log integrated EMG and percent displacement of skin landmarks. This relationship is defined as the "normal"standard against which data from patients can be plotted and judged. This system of evaluating facial motion, however, is extremely complicated and time consuming, and requires expensive EMG equipment and highly trained observers.
The Facial Nerve Function Index ("FNFI") was derived by Peckitt et al. by examining facial movement of 100 normal subjects and measuring on each side of the face the change in distance between the outer canthus of the eye and the lateral commissure of the mouth at rest and when smiling. See, N. Peckitt, R. Walker, G. Barker, The Facial Nerve Function Coefficient: Analysis of 100 Normal Subjects, 50 J. Oral Maxillofac. Surg. 338(1992), the disclosure of which is incorporated herein by reference. The FNFI, however, produces a skewed distribution making the FNFI awkward to interpret and limited in its usefulness to evaluate facial motion improvement. The Facial Nerve Function Coefficient ("FNFC") was subsequently formulated to provide a more symmetrical distribution of the FNFI with a more narrow reference range for evaluating facial movement recovery. The FNFC, however, is limited in that it does not provide for quantitation of a wide range of facial movements.
Manktelow et al. proposed a method for measuring facial movements during smile to assist a surgeon in assessing the results of facial reconstructive surgery. See R. Manktelow, J. Paletz, C. Guest, Quantitative Assessment of Smile Reconstruction in Facial Paralysis, 1991 Third Vienna Muscle Symposium 218, the disclosure of which is incorporated herein by reference. This method involves measuring the change in distance during smile between a selected fixed point on the face and the commissure or the mid-lateral point on the upper lip.
None of these quantitative methods, however, simultaneously measure facial movement in all facial zones under circumstances designed to provide the maximal, voluntary recruitment of neuromuscular units with the remainder of the face at rest (i.e. conditions which enable the detection and quantitation of synkinesis and/or normal associated movements, when present).